And here’s some calculations by someone who has had a physics class more recently than I have. In case you’re lazy, he posits 90 mph for a 4’ 2” x 4” on a typical saw. Significantly les than the ~150 mph theoretical limit, but still a lot of energy flying around ready to do damage to you and your shop.

Tom’s a good guy trying to help out the new woodworker. He even admits in the video how stupid it was, IIRC. It’s just another reminder to keep vigilant around tools. I believe the stat was that its the more experienced woodworker who receives the more serious injury as they become complacent around their tools.

I hadn’t seen that video before. Interesting and scary, and valuable as a teaching tool. I think the best take-home is how fast these things happen. It’s hard to make myself respect the fact that I won’t be able to snap my hand back out of the way of something happens. It takes a good 10 milliseconds just for the nerves to transmit the signal from your brain to your arm, which enough time for a 4400 rpm blade to go around about 3/4 of a revolution. That’s a lot of teeth.

As far as the physics calculations, that page neglects the fact that the motor is still supplying energy to the system even as the kickback is happening. It’s not just the inertia. I’d still like to see MythBusters take this one on.

What this guy neglected to guard against was the fact that he was applying downward pressure to the push block—in turn the push block is stopping that downward pressure—once the push block is gone his downward pressure is still being maintained—so he is effectively still applying a forward pressure.